Wireless communications systems are widely deployed to provide various telecommunications services such as telephony, video, data, messaging, and broadcast. Typical wireless communications systems may employ multiple-access technologies capable of supporting communications with multiple users by sharing available system resources (e.g., bandwidth, transmitting power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
When user equipment (UE) searches for an LTE cell, because the user equipment cannot know the center frequency of the LTE cell, the user equipment needs to scan the whole band. Therefore, the user equipment may spend a long time searching for an LTE cell. For example, as shown in FIG. 1A, when the user equipment perform carrier search in the LTE band X, because the user equipment doesn't have the information for the LTE cells. Therefore, even if the user equipment finds LTE cell 1, the user equipment still needs to detect other carriers in a LTE band X for searching for other LTE cells (e.g. LTE cell 2).
In addition, because 4G Radio Access Technology (i.e. Long Term Evolution (LTE)) needs to support more and more bands, many bands which support LTE may overlap with the bands which support 2G and/or 3G Radio Access Technology. In addition, due to spectrum re-framing, some 2G/3G bands will be re-used for deploying 4G, thus, it is possible 2G and 4G or 3G and 4G will be deployed on the same band. For example, as shown in table 1, the band 1805-1880 MHz may be deployed by 2G, 3G and/or 4G, the band 1905-1990 MHz may be deployed by 2G, 3G and/or 4G, and the band 2110-2170 MHz may be deployed by 3G and/or 4G.
TABLE 1DL freq. range (MHz)2G3G4G1805-1880GSM 1800WCDMA band3LTE band31930-1990GSM 1900WCDMA band2LTE band22110-2170xWCDMA band1LTE band1
Therefore, when the user equipment performs a carrier search in an LTE band, there may be a 2G/3G cell on the LTE band. The user equipment may spend long time detecting all cells in the LTE band, but can't search for a 4G cell in the LTE band. For example, as shown in FIG. 1B, when the user equipment performs carrier search for 4G cell in the LTE band X, because there are only 2G and 3G cell in the LTE band X, the user equipment can't search for a 4G cell in the LTE band X.